Another point about manufacturing jobs that I think a lot of people don't realize is that when the Bureau of Labor Statistics publishes data on manufacturing employment, they're relying on establishment data as coded by the North American Industry Classification System. That means they're not tracking job functions, they're tracking establishment functions. If you work in a hospital, you're in the Health Care and Social Assistance sector (code 62) most likely in 6221 General Medical and Surgical Hospitals. But that doesn't mean you're a doctor, you might work in the cafeteria. If you work in the cafeteria of a college, by contrast, you're an Education Services worker. If there's such a thing as in-factory cafeterias, then the people who work in them are manufacuring workers.
For many purposes, there's no alternative to relying on NAICS data. But this question of what kind of facility people are working in is almost certainly not the question you're interested in. Becoming a nation of doctors is very different from becoming a nation of hospital cafeteria workers. The overall quantity of janitors in the country is more interesting than whether the janitors work in factories or in office buildings. When a manufacturing firm stops using in-house accounts and instead contracts with an accounting firm, that's not a hollowing out of America's manufacturing capacities. Figuring out what's really happening is sometimes annoyingly difficult.